1. ULTIMATE: a High Resolution CMOS Pixel Sensor for the STAR Vertex Detector Upgrade Christine Hu-Guo on behalf of the IPHC (Strasbourg) CMOS Sensors group Outline  STAR HFT Upgrade: PIXEL detector  MAPS (Monolithic Active Pixel Sensors) requirements  Recent MIMOSA26 test results  Comparison between standard and high resistivity EPI layers  ULTIMATE design & optimisation  Summary + Future plans

2. STAR IPHC christine.hu@ires.in2p3.fr 2 20-24/09/2010 TWEPP 2010 STAR Heavy Flavor Tracker (HFT) Upgrade Physics Goals:  Identification of mid rapidity Charm and Beauty mesons and baryons through direct reconstruction and measurement of the displaced vertex with excellent pointing resolution TPC – Time Projection Chamber (main detector in STAR) HFT – Heavy Flavor Tracker SSD – Silicon Strip Detector IST – Inner Silicon Tracker PXL – Pixel Detector (PIXEL) Goal: Increasing pointing resolution from the outside in TPCSSDIST PXL ~1 mm~300 µm~250 µm vertex <30 µm courtesy of M. Szelezniak / Vertex-2010

3. STAR IPHC christine.hu@ires.in2p3.fr 3 20-24/09/2010 TWEPP 2010 STAR PIXEL Detector ~20 cm Cantilevered support One of two half cylinders RO buffers / drivers Total: 40 ladders Ladder = 10 MAPS sensors (~2x2 cm² each) Detector extraction at one end of the cone Sensors Requirements Multiple scattering minimisation:  Sensors thinned to 50 um, mounted on a flex kapton/aluminum cable  X/X 0 = 0.37% per layer Sufficient resolution to resolve the secondary decay vertices from the primary vertex  < 10 um Luminosity = 8 x 10 27 / cm² / s at RHIC_II  ~200-300 (600) hits / sensor (~4 cm 2 ) in the integration time window  Shot integration time ~< 200 µs Low mass in the sensitive area of the detector  airflow based system cooling  Work at ambient (~ 35 °C ) temperature  Power consumption ~ 100 mW / cm² Sensors positioned close (2.5 - 8 cm radii) to the interaction region  ~ 150 kRad / year  few 10 12 N eq / cm² / year 2.5 cm Inner layer 8 cm radius Outer layer End view Centre of the beam pipe courtesy of M. Szelezniak / Vertex-2010

4. STAR IPHC christine.hu@ires.in2p3.fr 4 20-24/09/2010 TWEPP 2010 STAR PIXEL Detector 3 steps evolution:  2007: A MimoSTAR-2 sensors based telescope has been constructed and performed measurements of the detector environment at STAR MimoSTAR-2: sensor with analogue output  2012: The engineering prototype detector with limited coverage (1/3 of the complete detector surface), equipped with PHASE-1 sensors will be installed PHASE-1: sensor with binary output without zero suppression  2013: The pixel detector composed with 2 layers of ULTIMATE sensors will be installed ULTIMATE: sensor with binary output and with zero suppression logic PIXEL detector composed of 2 MAPS layers Prototype detector composed of 3 sectors with PHASE-1 sensors 3 plans telescope with MImoSATR-2 sensors

5. STAR IPHC christine.hu@ires.in2p3.fr 5 20-24/09/2010 TWEPP 2010 MIMOSA26: Sensor for EUDET Beam Telescope Main characteristics of MIMOSA26 sensor equipping EUDET BT:  Column // architecture with in-pixel Amp & CDS and end-of-col. discrimination, followed by Ø  Active area: 21.2×10.6 mm²,1152 x 576 pixels, pitch: 18.4 µm   sp. <~ 4 µm  Read out time 10 6 particles/cm²/s  Yield ~90% ( 75% fully functional sensors thinned to 120 µm + 15% (showing one bad row or column)  Thinning yield to 50 µm ~90% Collaboration with IRFU/Saclay

6. STAR IPHC christine.hu@ires.in2p3.fr 6 20-24/09/2010 TWEPP 2010 MIMOSA26 with high resistivity EPI layer (1) Charge collection efficiency for the seed pixel, and for 2x2 and 3x3 pixel clusters Signal to noise ratio for the seed pixel before irradiation and after exposure to a fluence of 6 x 10 12 n eq / cm²

7. STAR IPHC christine.hu@ires.in2p3.fr 7 20-24/09/2010 TWEPP 2010 MIMOSA26 with high resistivity EPI layer (2) Beam test at CERN SPS (120 GeV pions)  Test conditions: 50 MHz to emulate the longer integration time in ULTIMATE 35 °C temperature! resolution < 5um

8. STAR IPHC christine.hu@ires.in2p3.fr 8 20-24/09/2010 TWEPP 2010 ULTIMATE: Extension of MIMOSA26 Half reticle 1152 x 567 pixel matrix Temperature ~20 °C Light power consumption constrains Space resolution ~4 µm No constrains on radiation tolerance Full reticle 960 x 928 pixel matrix  Longer integration time ~200 µs Temperature 30-35 °C Power consumption ~100 mW/cm² Space resolution < 10 µm 150 kRad / yr & few 10 12 Neq /cm² /yr  Optimisation 20240 µm 22710 µm 3280 µm 21560 µm 13780 µm MIMOSA26 ULTIMATE

9. STAR IPHC christine.hu@ires.in2p3.fr 9 20-24/09/2010 TWEPP 2010 ULTIMATE Design & Optimisation (1) Reduction of power dissipation:  Power supply voltage reduced from 3.3 to 3 V  Optimisation of pixel pitch v.s. non ionising radiation tolerance Larger pitch: 18.4 µm  20.7 µm  Shorter integration time: 185.6 µs  Validated by a small prototype  Optimisation of power consumption of some blocks  Estimated power consumption ~130 mW/cm² Pixel improvement: charge collection, radiation tolerance  High resistivity EPI substrate & radiation tolerance design Lab test with 55 Fe at 35 °C and integration time imposed by the STAR requirements shows:  Conversion gain is improved by a factor of two  ENC >~ 10 e - before irradiation  ENC >~ 13 e - after irradiation with 150 kRad  ENC >~ 16 e - after irradiation with 3 x 10 12 Neq/cm²  SNR up to 30 after irradiation SNR ~30 for standard resistivity EPI before irradiation Beam test measurements are in progress  Preliminary results show further performance improvements

10. STAR IPHC christine.hu@ires.in2p3.fr 10 20-24/09/2010 TWEPP 2010 ULTIMATE Design & Optimisation (2) Discriminator timing diagram optimisation  Threshold non-uniformity reduction Obtained timing diagram due to long track: - Mimosa26: Threshold dispersion of 1152 discriminators (divided in 4 groups) - It doesn't disturb chip operation if threshold is set to be higher than the dispersion Due to the delay, ex. charge injections by S3, S4 cannot be compensated by the auto 0 phase No. of discriminators discriminator 1152 discriminators Pixel Array ~2 cm drivers Ideal timing diagram: Optimised timing diagram: (validated by a proto)

11. STAR IPHC christine.hu@ires.in2p3.fr 11 20-24/09/2010 TWEPP 2010 ULTIMATE Design & Optimisation (3) On-chip voltage regulators  Interferences minimisation on critical nodes  Common power supply for A & D  Regulator: Low Dropout (Vin = 3 - 3.3 V) Characteristics: Dropout voltage: ~0.3 V, PRSS: ~40 dB, Noise: < 1 µV/sqrt(Hz) (freq at 10 KHz), Power consumption: <~ 1mW, For Pixels Clamping For Analogue Power Supply See Jia Wang's poster To Pixel Array & Column-level ADC Digital circuit Vdd Vdd_A Bias DAC Vdd_D Bias DAC Regulator V_clp Vdd_A Digital circuit Regulator V_clp Regulator

12. STAR IPHC christine.hu@ires.in2p3.fr 12 20-24/09/2010 TWEPP 2010 ULTIMATE Design & Optimisation (4) Zero Suppression circuit (SuZe) adapted to STAR condition  Higher hit density  larger memories  2 memories of 2048x32 bits  2 LVDS data out at 160 MHz Latch up free memory may be integrated in future chip  Prototype: SRAM memory module Size: 256 x 8 bits Area: 1000 x 375 µm² Self-timing for radiation tolerance Write Access Cycle: 4.3 ns Read Access Cycle: 4.4 ns Power consumption: 0.15 mA/MHz  A larger memory can be built by reorganizing the designed module [1] [1] K. Kloukinas, G. Magazzu, A. Marchioro, “A Configurable Radiation Tolerant Dual-Ported Static RAM macro, designed in a 0.25 µm CMOS technology for applications in the LHC Environment ”, 8th Workshop on Electronics for LHC Experiments, 2002 Compatible with IP block Memory cell

13. STAR IPHC christine.hu@ires.in2p3.fr 13 20-24/09/2010 TWEPP 2010 Summary + Future plans MAPS with high-resistivity epitaxial layer show excellent detection performances:  Detection efficiency >99.8% (at 10 -5 fake hit rate)  Improvement of radiation tolerance, non ionising radiation tolerance increased by O(10²) PIXEL detector for the STAR experiment based on ULTIMATE sensors will fulfil the STAR HFT requirement  ULTIMATE sensor is planned to be delivered to LBL in Q1 2011  400 sensors per detector Engineering prototype detector equipped with PHASE-1 sensors covering 1/3 of the complete detector surface, will be installed in 2012 (physics in 2013) Nominal detector installation is scheduled 2013 (physics in 2014)

14. STAR IPHC christine.hu@ires.in2p3.fr 14 20-24/09/2010 TWEPP 2010

15. STAR IPHC christine.hu@ires.in2p3.fr 15 20-24/09/2010 TWEPP 2010 Milestone: CMOS Sensors for the STAR PXL detector LBNL-IPHC collaboration on vertex detector upgrade of STAR experiment (RHIC)  PXL: 2 layers equipped with 10/ in + 30/ out ladders, each made of 10 sensors designed by IPHC  CMOS pixel sensors  breaking edge technology: granular, thin, swift, low power November 2009: technological choice of PXL discussed in CD-1 review  formally approved in Spring 2010  1st vertex detector ever operated with CMOS sensors 2009/2010 activities on 2 generations of sensors :  PHASE-1 (physics in 2013): validated & integrated on ladders at LBNL  ULTIMATE (physics in 2014): 4 times faster, more radiation tolerant, etc. design under way in a new fabrication technology main innovative features w.r.t. PHASE-1 validated on prototype tested at CERN-SPS Next steps :  submission of ULTIMATE sensor in December 2010 tests in Spring 2011  contribution to ladder testing  contribution to STAR central software development for tracking in PXL